Vacuum plasma generators are known to have various power ratings and to provide various signal output forms. In vacuum glass coating, for example, generators having DC output and medium frequency (MF) output with power ratings between 30 and 300 kW are used. The MF signal at the output of the generator is in most cases a sine signal with frequencies between 10 kHz and 200 kHz. In this case, the output voltages can be from several 100 V to more than 1000 V. For ignition of the plasma, the output voltages from the generators are often higher than in normal operation.
Vacuum plasma generators can also generate signals that can interfere with the functioning of other devices within the vacuum plasma system. For example, voltage converter circuits within the vacuum plasma generator can cause harmonics on a mains input connector that feeds the vacuum plasma generator. These harmonics, in turn, couple, through a mains connector and a mains power supply, to other devices in the vacuum plasma system and can interfere with these other devices.
High-frequency interference can occur on an output connector of the VPG upon ignition of the plasma. In this case, the cables, that is, the connection cables from the output of the VPG to electrodes of the plasma chamber, the cables for remote control of the VPG, and the cables of the mains supply, act as antennae that radiate high frequency (HF) power generated by the VPG. Depending on the length of the output cable between the VPG and the plasma chamber, such HF interference can be emitted into and captured from the surroundings, and therefore interfere with the functioning of other devices in the plasma system.
The cables also act as receiving antennae, that is, they also capture HF power and couple it into the VPG and may in that manner interfere with its operation. Here too, the length of the conductors and the frequency of the interference are factors that can impact the level of interference. Interference can also be coupled into the VPG directly from the mains power line. Additionally, there are also voltage surges, voltage sags, and also momentary interruptions in the mains power supply that can adversely affect the functioning of the VPG.
A high-power, medium-frequency generator for plasma systems is described in German Utility Patent DE 298 19 336 U1, in which the vacuum plasma generator is divided into a mains power supply part and an oscillator arrangement, and the oscillator arrangement is matched to the external geometry of the coating chamber, and is mechanically and electrically connected directly to a magnetron disposed in the plasma chamber.